Modern wireless communication devices often operate in mixed radio access technology (RAT) environments in which multiple RATs are deployed with overlapping coverage areas. For example, Long Term Evolution (LTE) networks can be deployed in overlapping regions with second generation (2G) and third generation (3G) RATs, including Universal Mobile Telecommunications System (UMTS) networks and Global System for Mobile Communications (GSM) networks. As such, a wireless communication device supporting operation over multiple RATs can select a RAT to use for network access, and can transition between RATs as the device moves between coverage areas through an IRAT transition procedure.
In current IRAT decision making for performance of a reselection or handover, only signal strength is considered. As such, there are situations in which IRAT transition can be triggered when a user can still get a good experience for active data traffic in the serving RAT even though the signal strength of the serving RAT may be below a threshold for triggering an IRAT reselection or handover. IRAT activities result in significant traffic discontinuity due to cell selection procedures and signaling exchanges, such as location update (LU) and routing area update (RAU), that are performed attendant to transitioning from a serving RAT to a target RAT. As such, user experience during an IRAT transition procedure can suffer, as data traffic discontinuity can interrupt and delay user activities.
Moreover, just because a target RAT has better coverage than a serving RAT does not mean that the target RAT will support a sufficient QoS. For example, a 2G RAT cell can have a broader coverage area than a 3G or LTE RAT cell, and thus may generally have the best signal strength of available RATs. However, a 2G RAT may not offer a better QoS than 3G or LTE, even if the signal strength of the 2G RAT is stronger than a serving RAT.